To minimize the BEOL interconnect portion of circuit delay, a conventional SiO2 dielectric (k˜4.0) has been replaced with dense lower-k films (K<3.0). However, for even further performance improvement, more parasitic capacitance reduction is required (k<2.5) for high-speed circuits. Most of the porous low-k dielectric materials, though, have relatively weak mechanical properties as compared to dense dielectrics. As such, it has become a significant challenge for current BEOL processes to integrate these materials with other module processes. For example, the conventional chemical-mechanical polish process has difficulty polishing porous dielectrics, and the conventional PVD diffusion barrier deposition technology cannot offer reasonable coverage on the surface of porous dielectrics.
Moreover, it has been found that when the dielectric constant of an insulator in an interconnect structure is reduced, mechanical properties are often compromised, giving rise to significant challenges in interconnect integration and reliability. By way of illustration, due to low adhesion of the dielectric an interfacial crack may occur during fabrication. This is a particular problem in the fabrication of multilevel interconnected integrated circuits since it can significantly reduce yield and impair reliability of the device.
In one example, to increase throughput, a plurality of integrated circuits are fabricated on a wafer, in parallel, using porous low-k dielectrics. The integrated circuits are then separated into individual chips using a process known as “dicing.” However, as the kerf is diced, cracks and delaminations can be generated that can propagate into the active chip regions. This has been found to be especially problematic in multilevel devices where the dielectric constant of the insulator in an interconnect of the integrated circuit is reduced, mainly due to the mechanical properties of the insulator. Cracks in excess of a few microns in depth and several tenths of millimeters in length have been observed. The cracks and delaminations can either result in chip yield loss or reliability issues as the chip is stressed in a package.
To combat this problem, an air gap between the diced channel and the active chip region is fabricated using conventional RIE (reactive ion etching) processes. By way of illustration, after the multilevel interconnected chip is fabricated, a single RIE process is used to etch through all of the layers, preferably to the first capping layer above the first dielectric. By using the crack stop (e.g., air gap), it has been found that the cracks and delaminations will terminate at the crack stop, prior to reaching the active chip area. That is, the crack stop will eliminate or significantly reduce the crack/delamination driving force such that the propagation of the crack/delamination will be stopped prior to reaching the chip active area.
However, in current RIE processes, the size of the crack stop design tends to be fairly wide, on the order of approximately 10 um. This is mainly due to the fact that RIE cannot effectively etch through several layers of dielectric, etc. without also increasing the width of the resultant trench. Without increasing the width of the trench, for example, the conventional RIE process cannot etch through all of the levels of the interconnected circuit, in particular the lower levels, and hence cannot effective stop the propagation of the crack.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.